A Boeing 777 Malaysian airlines plane has reportedly been shot down along the Russian-Ukrainian border, according to an official from Ukraine's Ministry of the Interior.

The border is currently a war zone with sustained fighting between the Ukrainian government and pro-Russian separatist rebels. And within the past month, the separatists have brought down a number of Ukrainian military aircraft.

The cause of the crash isn't conclusively known at the moment. Pro-Russian separatists may have nothing to do with it. But they have been successful in destroying aircraft in recent months of the conflict.

Armed with Man-Portable Air Defense Systems (MANPADS), the separatists have been taking down Ukrainian military aircraft since the beginning of June. On June 13, separatists shot down a Ukrainian transport plane that had been carrying 40 paratroopers and nine crew members.

At least 10 other Ukrainian aircraft — all of them significantly lower-flying than a Boeing 777 — have been shot down since the rebels started using MANPADS according to a count kept by military aviation expert David Cenciotti, including five Mi-24 Hinds, two Mi-8 helicopters, one An-2, one An-30, and the Ukrainian transport plane.

Pro-Russian rebels claimed responsibility for shooting down two additional Ukrainian Su-25 fighters on Wednesday. The Ukrainian Defense Ministry reported that one of the jets was hit by a portable surface-to-air missile.

According to an adviser to the Ukraine Interior Minister, the Malaysia plane was shot down by a Buk ground-to-air missile system. These systems require additional training to use and are launched from trucks. The AP saw a launch system resembling Buk missiles in the pro-Russian held Ukrainian town of Snizhne early Thursday.